This invention relates to tennis racquets, and, more particularly, to a tennis racquet having a frame with a cross sectional shape which optimizes the stiffness and torsion characteristics of the racquet.
The force applied by a tennis ball to a strung tennis racquet bends the racquet primarily in a plane which extends perpendicularly to the strung surface (primary mode bending). As the point of impact of the ball moves away from the longitudinal centerline of the racquet, the racquet tends to twist upon ball impact. This twisting or torsional movement increases as the distance of the point of impact from the longitudinal centerline increases. The bending and twisting causes deflection of the racquet, which reduces the power and accuracy that a player can impart to the ball.
Prior art tennis racquets designed to minimize bending and twisting often include a frame with an increased height when viewed in side elevation. Such racquets have increased stiffness in the primary bending mode, but they do not significantly reduce the twisting.
Kuebler U.S. Pat. No. 4,664,380 describes a dual taper beam tennis racquet. When viewed in side elevation, the frame has a maximum height in the area where the yoke portion and the Y-shaped throat portion merge with the inverted U-shaped portion of the head. The height decreases or tapers downwardly toward the top of the head and toward the handle, which is the basis of the xe2x80x9cdual taperxe2x80x9d description.
Wilson Sporting Goods Co. has sold a number of tennis racquets under the names Hammer and Sledge Hammer which have a dual taper. Some of the properties of those racquets are described in U.S. Pat. No. 5,368,295.
Wilson Sporting Goods Co. has also sold tennis racquets having the properties described in co-owned U.S. patent application Ser. No. 569,348, filed Aug. 21, 1990. Such racquets can be referred to as quad taper racquets because the width or thickness of the frame when viewed in plan also tapers in two directions. The maximum width of the frame is generally in the area of the maximum height, and the width decreases or tapers downwardly toward the top of the head and toward the handle.
Increased height of a racquet (viewed in side elevation) generally provides increased stiffness, i.e., resistance against primary mode bending. A circular cross section or a wider frame thickness (viewed in plan) provides increased torsion, i.e., resistance against twisting. However, a circular cross section is not as resistant to bending as a beam with a greater height.
The area of maximum twisting is generally just above the area where the yoke and Y-shaped arms of the throat merge with the inverted U-shaped portion of the head. In a dual taper or quad taper racquet frame, that area generally does not have enough width to provide optimum resistance to twisting. In a racquet having a round cross section, that area generally does not have enough height to provide optimum resistance to bending.
We have found that resistance against twisting of a tennis racquet frame can be increased by increasing the width of the frame, particularly just above the area where the yoke and Y-shaped arms of the throat merge with the inverted U-shaped portion of the head. Good resistance against both twisting and bending can be obtained by providing the frame with a more rectangular or boxier cross section having a greater width and smaller height than that of prior dual taper or quad taper racquets or other types of racquets in the area just above the merger of the yoke, Y-shaped throat, and the inverted U-shaped portion of the head. The width is preferably at least 0.600 inch, and more preferably at least about 0.640 inch. The ratio of the width and the height is at least 0.50, and more preferably at least about 0.54. The width of the cross section decreases toward the top of the head and toward the handle. The increased resistance to twisting permits the frame to be made wider, thereby increasing the maximum width of the strings and increasing the polar moment of inertia of the racquet. The more rectangular shape of the cross section provides better resistance against bending compared to an oval cross section.